INTRODUCTION
This handbook is designed as a quick and ready reference of weed control practices used in various cropping systems or site/situations in Oregon, Washington, and Idaho. Because chemical regulation of plant growth is complex and requires considerable knowledge, a large portion of the handbook is devoted to registered uses of herbicides, crop desiccants, and some plant growth regulators. Most uses of chemical regulators are based on research results of the Agricultural Experiment Stations or the Oregon State University Extension Service and the neighboring states of Idaho and Washington where circumstances are similar. Otherwise, a few suggestions are included from research conducted in other states or from U.S. Department of Agriculture Research Centers. In all cases, authors make every effort to list only registered herbicides and to ensure that the information conforms to product labels and company recommendations.
Intended Users  The handbook was originally planned as a manual for county Extension agents. However, the handbook also may be useful to company field representatives, commercial spray applicators and consultants, herbicide dealers, teachers, and some producers. Persons needing similar information pertaining to a few crops, sites, or situations should request Extension bulletins, fact sheets, or chapters from this handbook from their local county Extension office. Costs for publication and copying should be expected.
Revision and Availability  The handbook is revised and reissued annually.
Caution!
This handbook is not intended as a complete guide to herbicide use.
Before using any chemical, read the label on the container. Before a chemical can be recommended for a specific use, it must be thoroughly tested. The recommendation on the manufacturer’s label, when followed, can prevent many problems arising from the wrong use of a chemical.
Information is supplied here with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied. Trade names (brand names) of some commercial pesticides are used in portions of this handbook to help identify the common name used by the Weed Science Society of America (WSSA). Authors have assembled the most reliable information available to them at time of publication. Due to constantly changing laws and regulations, authors can assume no liability for the recommendations. Any use of a pesticide contrary to instructions on the printed label is not legal or recommended.
Weed Management Options: A Quick Guide
Prevention
Avoid weed establishment; eliminate individual survivors. 
Identify and map weed infestations; keep records over years.
Recognize and eliminate new weeds before they multiply and establish.
Employ sanitary procedures; prevent weed spread.
•	Clean equipment between sites or infestations.
•	Examine nursery plants, seed, and imported soil or media.
•	Screen irrigation water where weed seed contaminates surface water transported in canals and rivers or stored in lakes or ponds.
Control weeds and seed sources around the field or site.
Establish county and state weed laws and noxious weed control programs.
Biological
Manage other organisms against weeds.
Animals
•	Geese (dormant strawberries, asparagus, peppermint, caneberries, and trees; avoid during harvest season of crops except orchards).
•	Pigs (fallow only; reduce yellow nutsedge infestations).
•	Sheep and goats (control many weed and brush species; may compact soil in orchards).
Insects (classical approach; development costs require use on extensive areas; insect populations lag behind weed population and may be too slow for intensive or high-value cropping systems).
•	Klamathweed beetle on St. Johnswort (also called Klamathweed or goat weed).
•	Cinnabar moth and ragwort flea beetle on tansy ragwort.
•	Others (see “Biological Control” section in this Handbook).
Diseases (several examples exist of fungal and bacterial cultures for spraying to suppress or kill certain weeds; however, none in Pacific Northwest).
Cultural
Integrate numerous components to minimize impact of weeds.
Select manageable fields (identify weeds and choose crop according to feasibility of weed management strategies; e.g., avoid planting onions into perennial weeds).
Rotate crops (disrupt weed life cycles or suppress weeds in competitive crop followed by planting a noncompetitive crop).
Plant winter cover or competitive fallow crops in rotation to improve soils and crop management (specific cultivars are being evaluated).
•	Consider legumes to supplement nitrogen requirements.
•	Consider specific varieties of cereals with natural plant toxins (allelopathy); vegetation must remain uniform on soil surface; either perennial or large-seeded crops can be planted through undisturbed mulch.
•	Consider crops or cultivars that winter kill after vigorous growth during fall to avoid springtime controls.
Alter planting dates (plant for maximum growth or delay planting to control first weed flush).
Transplant slow-growing crops.
Place and time fertilizer, especially nitrogen.
•	Band or spot fertilizer beside plant or seed (reduces availability to surface-germinating weeds).
•	Time additional side-dressings for maximum crop growth or to minimize weeds.
Develop crop canopy that shades weeds or suppresses weed germination.
•	Select crops or varieties that form canopy quickly.
•	Space plants in equidistant (triangular) arrangements and vary density depending on crop management constraints or harvest requirements (e.g., product quality).
•	Interplant crops in space and time (consider mechanical limitations in commercial plantings).
•	Combine broadleaf and taller, narrowleaf crops (corn or beans with pumpkins).
•	Relay plantings or harvest short-duration crops within longer maturing crops (bush beans with corn; cucumbers with peppers; tree crops with vegetables).
•	Manage appropriate living mulch (grass or legume) between perennial crop rows.
•	Improve pasture management by reseeding and/or fertilizing with or without control measures to reduce weed infestation (weeds often are a symptom of poor management).
Apply mulch or geo-textiles
•	Organic materials
—Straw (may reduce available nitrogen when decomposing; often infested with weed seed).
—Sawdust (avoid vertebrate pests by maintaining mulch-free circle around tree; perennial weeds can become a serious problem).
—Bark mulch.
—Newspapers (during emergence, rhizomes of some perennial weeds become disoriented when penetrating 6 to 16 layers of overlapped newspaper).
•	Plastic
—Black excludes light, controls most annual weeds.
—Clear acts like greenhouse; poor weed control. New wavelength-selective plastics for pest management (research is progressing).
•	Geo-textiles (available at ag and garden supply stores)—Spunbonded fabrics (nonwoven):  lightweight, extruded polypropylene fibers; requires mulch cover due to moderate UV light sensitivity; weed roots and rhizomes can penetrate fabric unless removed before establishment; cheapest option.
—Woven fabrics:  moderate-weight polypropylene fibers woven into a mat; can be used without mulch cover due to UV light stability; weed roots and rhizomes can penetrate fabric although tightness of weave can prevent some weeds; moderate cost.
—Laminates:  highly porous, dense poly film bonded to capillary fibers with a pressed, nonwoven bottom layer. Surface is slick and causes rapid wetting and drying to prevent weed establishment, except for perennial rhizomes that can penetrate the laminate; most expensive geo-fabric.
•	Solarization  Thin plastic secured tightly over loose, moist soil for 8 to 12 wk during the hot seasons (July 15 through September 15) will provide good control of small-seeded weeds, particularly winter annuals such as annual bluegrass (Poa annua), even when used west of the Cascades. Also controls and/or suppresses some diseases.

Mechanical
Weed debris turned under; annual weeds controlled; perennial weeds suppressed if repeated every 10 to 14 days.
Tillage practices
•	Seedbed preparation/planting (plow down/mix debris). Plow, rototill, disc, harrow (compacts wet soils).
•	Cultivation for weed control. Sweeps, rolling cultivators, finger weeders, push hoe, rotary hoes, etc.
•	Hand pulling or hand hoeing.
Minimum or no-till systems (often requires specialized equipment).
•	Seedbed preparation/planting accomplished in one operation where trash is separated, soil loosened, and crop planted.
•	Weed control achieved with herbicides or sometimes cultivators, depending on debris.
Flaming (requires difference between crop and weed growth or crop protection with hooded row cover or protein foaming agents).
Hot water or steam (a nonselective treatment for broadleaf weeds and some grasses; requires tremendous energy to generate heat).
Water management (drip placement or timing to reduce weed growth).
Stale seedbed (planting after controlling first weed flush).
Herbicidal
Requires precise calculations, equipment, and application.
Selectivity
•	Crop naturally tolerates herbicide (internal selectivity).
•	Placement of herbicide prevents crop exposure.
•	Timing of application to avoid susceptible stage of growth.
Labeling requires extensive testing.
•	Toxicology includes acute, subacute, and chronic toxicity; teratology (fetus); reproduction, mutagenicity (cancer); neurotoxicity (nerves); and metabolism studies along with worker exposure.
•	Environmental fate includes breakdown, groundwater, ecological effects on plants and animals.
•	Tolerance assessment considers normal application procedures and preharvest intervals for assessing residues within food products. 

Year-Round Weed Management Strategies: A Summary 
Prevention
Employ sanitary practices; prevent new weed infestations. Prevent weed shifts resulting from repeated:
•	Cultivation (enhances perennial weeds).
•	Mowing (enhances prostrate weeds).
•	Herbicides (enhance tolerant weeds, new weed biotypes, new microorganisms that render herbicide inactive).
Identify and Map
•	Use reference books to help identify annual and perennial weeds.
•	Map and record infestations (weed abundance).
•	Keep yearly records.
Prioritize Weeds (develop thresholds)
•	Highly competitive weeds (control).
•	Moderately competitive weeds (suppress).
•	Low-growing or noncompetitive weeds (don’t worry).
List Controls
•	Your experience.
•	Local experts.
•	Published information.
•	Learn strengths and weaknesses of each control method.

Design Weed Management Program
•	Select fields or garden area with manageable weed species.
•	Consider environmental aspects: Erosion potential. Surrounding water, high-value vegetation, or urban and/or recreational areas.
•	Consider costs, equipment, skills, precision timing, and other factors needed to achieve results.
•	Develop year-round weed management strategies involving combinations of weed control practices.
Evaluate Results
•	Evaluate weed management programs.
•	Continue mapping weeds for future reference.
•	Modify practices as weeds shift because of repeated practices.